To perform cardiac pacing, a lead system is typically positioned in the right chambers of the heart (i.e. right atrium and/or ventricle) through the superior vena cava (SVC). Sometimes, it is desirable to perform sensing, pacing, and/or defibrillation of the left atrium and/or ventricle. However accessing the left chambers of the heart is more difficult than accessing the right chambers of the heart. The left ventricle is a high-pressure chamber which pumps oxygenated blood through the arteries to the furthest extremities of the body. Dislodgment of any portion of the lead located in the left atrium and/or ventricle may result in immediate patient death.
Access to the left chambers of the heart may be achieved through a thoracotomy or transvenous method. Due to the invasiveness and complications associated with a thoracotomy procedure it is desirable to use a transvenous approach.
Several difficulties are associated with placing a lead transvenously to stimulate the left chambers of the heart. Lead placement into the coronary sinus region is often hindered and, sometimes, obstructed by narrow pathways and curvatures. These narrow pathways and curvatures are inherent characteristics of coronary vessels. As used herein, the phrase “coronary sinus” or “coronary sinus region” refers to the coronary sinus vein, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the coronary sinus.
Several attempts have been made to provide a lead, which purports to anchor itself inside a coronary vessel, such as the coronary sinus. One such attempt proposes a lead which includes a coiled configuration and is described in U.S. Pat. No. 5,387,233 issued to Alferness et al. This kind of lead may be vulnerable to several problems when placed into the coronary sinus. In view of its helical structure, this lead may be more difficult to manufacture than ordinary leads. Moreover, the helical end of the lead may not maintain intimate or continuous contact with the inner wall of the vessel. The inability to maintain intimate contact may result from the difficulty of maintaining a geometrically uniform helical structure in the lead. The inability to maintain contact may also be due to inherent anatomical variations of coronary vessels. The lack of contact causes the lead to displace or dislodge from its position inside the vessel. Moreover, the lack of continuous contact with vessel wall makes it difficult to ensure proper contact of electrodes placed in the helical structure with the inner wall of the vessel. Lacking contact by the electrodes with the inner wall of the vessel renders cardiac stimulation ineffective or sensing inaccurate.
Hence, as noted above, adequate fixation of the lead and electrode in a coronary vessel is difficult to achieve. Like the posterior vein of the left ventricle, distal coronary vessel tributaries have small diameters. The leads placed in these vessels should track well and have a small diameter so they may be placed in distal vessels. The electrode should have intimate contact with the tissue and it should not dislodge. A small electrode, less than the diameter of the vessel, is likely to move easily within the vessel and may not be adequately affixed which results in displacement or dislodgment of the lead.
Thus, there is a need in cardiac pacing technology to be able to introduce and place a lead having one or more electrodes in regions of the heart having narrow pathways and variable curvatures. The lead should accommodate for placement in the coronary sinus region without experiencing displacement or dislodgment.